Electrochromism is a phenomenon in which a material exhibits a reversible electrochemically-mediated change in an optical property when placed in a different electronic state, typically by being subjected to a voltage change. The optical property is typically one or more of color, transmittance, absorbance, and reflectance. One well known electrochromic material, for example, is tungsten oxide (WO3). Tungsten oxide is a cathodic electrochromic material in which a coloration transition, transparent to blue, occurs by electrochemical reduction.
Electrochromic materials may be incorporated into, for example, windows and mirrors. The color, transmittance, absorbance, and/or reflectance of such windows and mirrors may be changed by inducing a change in the electrochromic material. One well known application of electrochromic materials, for example, is the rear view mirror in some cars. In these electrochromic rear view mirrors, the reflectivity of the mirror changes at night so that the headlights of other vehicles are not distracting to the driver.
While electrochromism was discovered in the 1960's, electrochromic devices have historically suffered from various problems that have prevented the technology from realizing its full commercial potential.